A screw type implant fixture includes a body having a screw thread formed on an outer surface and is used as a fixing unit to fix a dental or orthopedic prosthesis or the like into a bone. A bone tissue into which a fixture is to be inserted consists of cancellous and cortical bones. The cancellous bone refers to a relatively soft bone tissue of a bone, and the cortical bone refers to a relatively thin film, which is harder than the cancellous bone and generally encloses the cancellous bone. A length of the cancellous bone is usually longer than the cortical bone and thus the inserted fixture is implanted into the cancellous bone.
FIG. 1 illustrates an implant fixture 100 according to the conventional art. The implant fixture 100 includes a second portion 120 having a large screw thread 121 including peaks 121a and roots 121b alternating with one another on a central axis of the implant fixture 100, a first portion 110 disposed above the second portion 120 and including a smaller screw thread 111 than the screw thread 121 of the second portion 120, and a third portion 130 disposed below the second portion 120 and including a cave cutting portion 131 on the central axis of the implant fixture 100. A depth of a cave of the cave cutting portion 131 is longer than the bone of the third portion 130 so that the cave cutting portion 131 enables the implant fixture 100 to be easily inserted into a bone tissue at an initial stage. Also, outer diameters D1 of the first portion 110 and the second portion 120 are the same along the central axis.
The implant fixture 100 is inserted into an implant hole formed in a bone tissue of the human body using a drill. When the implant fixture 100 is inserted into the bone tissue, the third portion 130 and the first portion 110 are sequentially implanted into a cancellous bone, and the first portion 110 is implanted into a cortical bone. After the implantation is completed, bone tissues near the implant fixture 100 are grown to integrate with a surface of the implant fixture 100 to thereby fix the implant fixture 100.
However, the implant fixture 100 according to the conventional art has the following drawbacks.
First, the second portion 120 of the implant fixture 100 is not inserted into the bone tissue by sufficiently applying a pressure to the bone tissue, and thus the implant fixture 100 does not have a sufficient initial fixing force when the implantation is completed. Thus, bone absorption may occur near the implant fixture 100. The bone absorption is an atrophy due to a reduction in the amount of a bone tissue near the implanted implant fixture 100, which deteriorates the fixing force of the implant fixture 100, thereby hindering the whole stability of the implant fixture 100 or damaging a prosthesis attached to an upper end of the implant fixture 100.
Second, when a large implant hole is formed before the implant fixture 100 is inserted, osseointegration takes a long time and the initial fixing force is likely deteriorated as well. More specifically, such a large implant hole causes a bone tissue near the implant fixture 100 and the surface thereof to be far away from each other, which increases the amount of the bone tissue to be grown on the surface of the implant fixture 100, thereby increasing the total time for osseointegration.
Third, when an implant hole is not formed using a drill in a desired direction in a straight manner before the implant fixture 100 is implanted, if a thread has a stumpy peak cross section as shown in the conventional art, the implant fixture 100 is implanted in a wrong direction. More specifically, the implant fixture 100 follows a direction of the implant hole and has difficulties in changing a direction thereof to a desired direction or moving a position thereof. When the implant fixture 100 is implanted in a wrong position, it is necessary to remove the implant fixture 100 from the wrong position, form a new implant hole, and insert the implant fixture 100 into the new implant hole.